Regulating ballast for fluorescent lamps



REGULATING BALLAST FOR FLUORESCENT LAMF S Filed March 22, 1957 l T T F H at 15% l 25 L REF. NO. TURNS 32E? CA PTQ I W vours CURRENT OHMS mm. AMPERES i4 AB 3l5 L42 Ha L5 6 is ac I463 13.42 52B .795

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United States Patent This invention relates to ballasts for gaseous discharge lamps, such as fluorescent lamps, and to a system embodying the same.

It pertains more specifically to such ballasts as are of the high reactance step-up transformer type which supply the arc discharge device in series with a condenser. In such a circuit, the capacitive reactance predominates so that a ballast of this nature will have a power factor of the leading type probably lower than 90%. In order to correct the power factor of such a device, it is necessary to introduce lagging current or v.a. approximately equal to the leading current or v.a. This can be accomplished by introducing an air gap in the magnetic circuit of the transformer.

The present application is a continuation-in-part of my co-pending application, Serial No. 309,599, filed September 15, 1952, now abandoned, in which it is pointed out that improved results are obtained if the gap is a bridged gap which provides a magnetically saturated core portion. More specifically, said co-pending application discloses the use of a shell type core in which the bridged gap is in the form of a closed slot located in the winding leg, and it further points out that by proper location of the slot, greatly improved results can be obtained, particularly with respect to wave shape of the load current in a sequence start type of ballast which employs a starting winding.

According to the present invention, 1 have found with respect to a capacitive type ballast that it is possible to obtain certain improved characteristics when a plurality of slots in series with each other, are provided in the secondary portion of the Winding leg, particularly when the slots are of different length, since the variation in length of slot has a direct result on the area of the saturable portion. The term length" as used with respect to the slot refers to its longest dimension, which can be expressed as a percentage of the width of the winding leg, and the term Width as applied to the slot, refers to its shorter dimension which corresponds to the length of the air gap provided, this dimension being parallel to the longitudinal axis of the winding leg.

It has been further found, that where two or more slots are provided, which are of varying length, that improved results may be obtained by combining two of these slots into a single slot which is referred to herein as a T-slot, due to its shape.

In other Words, the present invention relates primarily to the combination of two slots of different length which may be either separate or combined. One more additional slot may be provided to improve certain characteristics, if required.

In the embodiment shown, the first and second slot are combined into a single T-slot, and the third slot is preferably separate in the form of an auxiliary slot, although it is also possible to combine the third slot with the first two slots.

The invention is herein shown with respect to a capacitive ballast of the rapid start type, which is to say a capacitive ballast which does not employ a separate starting winding. When the T-slot is applied to this type of ballast, the location of the T-slot will be considerably Get. 15, 1963 different from the location of the single slot as pointed out in the aforesaid co-pending application.

With reference now to the drawings in which like reference numerals designate like parts:

FIG. 1 is a plan view of the core structure showing the location of the primary and secondary windings in dotted lines;

PEG. 2. is a wiring diagram of the ballast; and

FIG. 3 is a table showing electrical values during operation.

With reference now to FIG. 1 which shows the core structure of the high reactance transformer, reference numeral It) designates the winding leg, and the reference numerals 11 and 12 designate the yoke portions. These elements are built up of laminations of the T and L types.

The resulting shell type core structure provides windows '13 in which are disposed the primary winding 14 and the secondary winding 15, both shown in dotted lines. In the particular design shown, no separate shunt portion is provided, since a leakage path 22 is provided by the mere juxtaposition of the two windings, although a magnetic shunt type of path may be provided if desired. Actually, the windings are spaced from each other by about a quarter inch, since in winding the coils the paper separator extends beyond each coil layer by approximately one-eighth inch.

Those portions of the winding leg which are surrounded by the primary and secondary windings can be referred to as the primary portion is, and the secondary portion 17' respectively.

A T-slot 18 is located in the secondary portion 17 at a position such that its effective center line is substantially 48 percent of the distance from the center line of the leakage path 22 to the remote end of the secondary core portion 17. An auxiliary slot 19 is provided which is located at substantially 12 /2 percent of this distance, these locations being identified in FiG. l.

The T-slot comprises a head portion 2d and a base portion 21, and the slot is preferably oriented so that the base portion extends toward the leakage path 22. The length of the head portion is preferably percent of the width of the winding leg, and the length of the base portion 21 and of the auxiliary slot 19 is preferably 57 percent of the width of the winding leg. Thus saturable core portions 23, 24, and 25 are provided, of which portions 23 and 24 are adjacent to each other. The provision of adjacent portions 23 and 24 of varying width has been found to improve the crestfactor of the load current very substantially by increasing the reluctance of the iron in the secondary flux path.

In the example shown, the Width of the head portion 29 is substantially .663 inch, the width of the base portion 21 is substantially .093 inch, and the width of the auxiliary slot 19 is substantially .040 inch.

In the example shown, the width of the winding leg is substantially 1.078 inches, and the length of the windows 13 is substantially 6.0 78 inches, of which the secondar portion of the winding leg is substantially 4 inches long. The core stack is 1 3 inches high.

As shown in FIG. 2, the primary and secondary windings M- and 15 are connected in auto-transformer relationship, and the circuit includes a condenser 26, and two fluorescent lamps 27 connected in series circuit with each other and with condenser 26 and the windings l4 and 1%. In the particular example herein shown, the lamps 27 are SOOMA rapid start lamps, type 96Tl2.

Although the present invention is not limited to components of any particular value or quantity, in the specific example shown herein, such values, during operation, are set forth in FIG. 3. In operation, it has been found that the device shown has the following operation characteristics:

Crest factor (ratio of peak current to R.ld.S.) Power factor 1.55 percent 94 The voltage drops in H6. 3 are taken across the correspondingly indicated points in FIG. 2, and in certain instances, the resistance, and the capacity of the various elements are also shown.

The T-slot improves the crest factor, provides greater load wattage, provides a cooler running ballast, and provides a ballast of overall improved power factor.

The subject matter of the aforesaid co pending application is incorporated herein by reference, insofar as consistent with the present disclosure.

Although only a preferred embodiment of my invention is shown and described herein, it will be understood that modifications and changes can be made in the embodiment shown Without departing from the spirit of my invention as pointed out in the appended claims.

I claim:

1. A capacitive type series ballast for a fluorescent lamp comprising a primary winding, and a, secondary winding, a core structure, the core structure having a winding leg and a yoke portion and the primary and secondary Windings being axially adjacent to each other on said winding leg to provide [a flux leakage path therebetween, said core being divided into primary and secondary portions by said flux leakage path, said core structure having slot means formed in said secondary portion, said slot means comprising a closed T-sl-ot comprising a head portion and a base portion, the longitudinal axis of said head and base portions being substantially perpendicular to the longitudinal :axis of said winding leg, and the length of said head portion being greater than the length of said base portion so as to provide two saturable core portions of different cross sectional areas which are adjacent to each other.

2. A capacitive type series ballast for a fluorescent lamp comprising a primary winding, and a secondary winding, a core structure, the core structure having a winding leg and a yoke portion and the primary and secondary windings being axially adjacent to each other on said Winding leg to provide a flux leakage path therebetween, said core being divided into primary and seconda-ry portions by said flux leakage path, said core structure having slot means formed in said secondary portion at a point offset from said flux leakage path by substantially 48% of the length of said secondary portion, said slot means comprising a closed T-slot comprising a head portion and a base portion, the longitudinal axis of said head and base portions being substantially perpendicular to the longitudinal axis of said Winding leg, and the length of said head portion being greater than the length of said base portion so as to provide two satura-ble core portions of different cross sectional areas which are adjacent to each other.

3. A ballast as claimed in claim 2 in which said core structure has an auxiliary slot formed in said secondary portion at a point offset from said ilnx leakage path by,

substantially l2 /2% of the length of said secondary portion, the longitudinal axis of said auxiliary slot being substantially perpendicular to the longitudinal axis of portion is substantially 57% of the width of said Winding leg.

6. A ballast as claimed in claim 5 in which said core structure has an auxiliary slot formed in said secondary portion at a point offset from said flux leakage path by substantialy l2 /2% of the length of said secondary portion, the longitudinal axis of said auxiliary slot being substantially perpendicular to the longitudinal axis of said winding leg, and the length of said auxiliary slot being substantially 57% of the width of said winding leg.

7. A high reactance ballast transformer comprising a shell type magnetic core having an elongated central core leg and a pair of yoke core legs defining coil receiving windows with said'central core leg, a primary winding and a secondary winding arranged on side-by-side portions of said central core leg within said windows, said central core leg having a pair of spaced transverse slots forming bridged-gaps in the magnetic circuit of said secondary winding, one of said bridged-gaps being proximate to said primary winding and affecting the current thereof.

8. The high reactance ballast transformer of claim 7 wherein the other bridged-gap is located remote from said primary winding to have relatively little effect upon the current thereof.

9. The high reactance ballast transformer of claim 8 wherein the percentage of core restriction provided by said proximate bridge-gap is less than the core restriction pro vided by said remote bridged-gap.

10. A high reactance ballast transformer comprising a shell type magnetic core, having an elongated central core leg and a pair of yoke core legs defining coil receiving windows with said central core leg, at primary winding and a secondary winding arranged on side-byside portions of said central core leg within said windows, said central core leg having a pair of spaced transverse slots forming bridged-gaps in the magnetic circuit of said secondary winding, one of said bridge-gaps being no more than 20% of the length of the secondary winding away from saidprimary winding, and the other bridged-gap being no less than 30% of the length of said secondary winding away from said primary winding. I

11. The high reactance ballast transformer of claim 10 wherein said primary and secondary windings are connected in autotransformer relationship.

12. The high reactance ballast transformer of claim 10 wherein the percentage of core restriction provided by said bridged-gap closer to said primary winding is less than the percentage of core restriction provided by said bridged-gap more remote from said primary winding.

13. A high reactance ballast transformer comprising a shell type magnetic core having an elongated central core leg and a pair of yoke core legs defining coil receiving windows with said central core leg, a primary Winding and a secondary winding arranged on side-by-side portions of said central core leg Within said windows, said central core leg having a pair of spaced transverse slots forming bridged-gaps therein, one of said slots being located essentially in the magnetic circuit of said secondary winding only and the other of said bridged-gaps being located in the magnetic circuit of both said primary and secondary windings.

l4. Ballast apparatus for starting andv operating fluorescent lamps comprising a high reactance transformer including a shell type magnetic core having an elongated cent al core leg and a pair of elongated yoke core legs defining coil receiving Windows with said central core legs, a primary winding and a secondary winding arranged on side-by-side portions of said central core leg Within said windows, a capacitor connected in series with said secondary Winding for connection in series with a fluorescent lamp across said primary winding, and said central core leg having a pair of spaced transverse slots forming bridged-gaps therein, one of said bridged-gaps being located essentially in the magnetic circuit of said secondary winding only, and the other bridgedgap being References Cited in the file of this patent UNITED STATES PATENTS Boucher Mar. 13, 1934 Sola Apr. 11, 1944 Brooks Dec. 11, 1951 Howelett Mar. 3, 1953 FOREIGN PATENTS Australia July 3, 1947 

14. BALLAST APPARATUS FOR STARTING AND OPERATING FLUORESCENT LAMPS COMPRISING A HIGH REACTANCE TRANSFORMER INCLUDING A SHELL TYPE MAGNETIC CORE HAVING AN ELONGATED CENTRAL CORE LEG AND A PAIR OF ELONGATED YOKE CORE LEGS DEFINING COIL RECEIVING WINDOWS WITH SAID CENTRAL CORE LEGS, A PRIMARY WINDING AND A SECONDARY WINDING ARRANGED ONE SIDE-BY-SIDE PORTIONS OF SAID CENTRAL CORE LEG WITHIN SAID WINDOWS, A CAPACITOR CONNECTED IN SERIES WITH SAID SECONDARY WINDING FOR CONNECTION INSERIES WITH A FLUORESCENT LAMP ACROSS SAID PRIMARY WINDING, AND SAID CENTRAL CORE LEG HAVING A PAIR OF SPACED TRANSVERSE SLOTS FORMING BRIDGED-GAPS THEREIN, ONE OF SAID BRIDGED-GAPS BEING LOCATED ESSENTIALLY IN THE MAGNETIC CIRCUIT OF SAID SECONDARY WINDING ONLY, AND THE OTHER BRIDGED-GAP BEING LOCATED IN THE MAGNETIC CIRCUIT OF BOTH SAID PRIMARY AND SAID SECONDARY WINDINGS. 